The present invention relates in general to the field of hypodermic needles, and in particular, to an injection device having a syringe body and a needle carriage disposed in a needle housing on one side of the syringe body.
The hypodermic needle is one of the most useful and common tools in modern medicine, but it is also one of the most dangerous. Common microorganisms, including deadly viruses, are known to be communicable through infected hypodermic needles. In the urgent environment of ambulances or hospital emergency rooms, used and exposed hypodermic needles present a hazard to medical workers or patients. An accidental stab or scratch produced by such needles can introduce dangerous viruses or other contaminants directly into a person's blood stream. Therefore, there is a need for protecting medical personnel and patients from exposed hypodermic needles.
Many solutions have been proposed to solve the problem. Most involve very complex, spring-loaded mechanisms for automatic needle retraction after injection. These are unsuitable for disposable syringes because of cost considerations. In addition, their intricate construction increases the chances of malfunctioning.
Another group of solutions proposes a manual retraction systems. These tend to be very inconvenient and cumbersome to operate. The number of steps to be performed by the person administering an injection is drastically increased. In addition, manual retraction systems, as well as the automatic ones referred to above, increase the number of parts on the front of the syringe barrel. This limits the range of angles from which the needle can be introduced under the patient's skin. In fact, with all the fixtures and attachments required for safe needle retraction, the operator is restricted to a ninety degree angle of entry. Under this angle the needle penetrates deep under the patient's skin and is frequently hard to withdraw.
Of course, the advantage of a shallower angle of entry has been recognized in the art. Many old-fashioned syringes have a needle-mounting snout located off-center for this very reason. Nonetheless, for technical reasons having to do with the retraction mechanism, no state of the art solution incorporates the concept of shallow entry angle and protection of the hypodermic needle.
Hypodermic syringes having pre-filled barrels and pre-filled cartridges for use with syringe systems provide an alternative to filling the hypodermic needle on site. Pre-filled syringes minimize packaging by eliminating the need for a separate vial of medication. This is of particular importance in the emergency room or ambulance where a variety of equipment must be stored in a limited area. In addition, the step of transferring the medicine from the vial to the syringe is eliminated. Reducing the number of steps required for an injection is of particular importance in the emergency room, hospital, ambulance or other environment where the medicine must be injected as quickly as possible. The large-bore needles used to extract the fluid from the vial are also eliminated, reducing the risks of accidental needle pricks during the handling of the syringe. The risk of contamination of the medicine is also reduced.
With many pre-filled syringes, the barrel includes a membrane which seals the liquid within the barrel. The membrane may be ruptured, releasing the fluid for injection, by using a needle assembly to pierce the membrane or by applying sufficient pressure to burst the membrane. Typically, the pre-filled syringe is supplied with the plunger projecting from the rear of the barrel, requiring additional space for packaging, shipment and storage of the device. Additional packaging may be required to secure the plunger in the extended position and prevent premature emptying of the barrel. Moreover, care must be taken to prevent damaging the plunger prior to use. Some available syringes include an outer shell which is coupled to a piston head. The fluid is dispensed by sliding the outer shell relative to the barrel to depress the piston head. Although this type of pre-filled syringe may be less susceptible to damage, the outer shell must be retained in an extended position until the syringe is used.
Pre-filled cartridges provide protection against contamination of the medicine and minimize the space required for storage and shipment of the cartridges since the cannula and plunger elements are separate from the cartridge. However, the overall space occupied by the different components of the syringe assembly is not reduced. Further, the pre-filled cartridge must be loaded into a syringe assembly prior to use, requiring an additional step. The risk of contamination may also be increased unless care is taken to protect the critical surfaces of the syringe assembly and/or cartridge from airborne contaminants.
U.S. Pat. No. 5,263,942 shows an example of a syringe which includes barrel housing the fluid chamber and a needle assembly guide which is formed as a one-piece molded extension of the barrel. The barrel wall is formed with a port to allow fluid to flow between the chamber and the needle assembly. In order to form this port, an access opening must be formed in the outer wall of the needle assembly guide to permit molding of the opening in the barrel wall. Forming a hole in the exterior wall of the guide provides potential contaminants with direct access to the port in the barrel wall, creating the risk the contaminants will mix with the fluid as it flows into the needle for injection. Moreover, the formation of the port in the barrel wall requires the use of a slide mold to create the openings, significantly increasing the cost of manufacture.